This invention relates to multi-component pressure-sensitive adhesives. More specifically, this invention relates to composite pressure-sensitive adhesives containing two main polymer components, which may be present in different layers in a multilayer structure or as a mixture.
Pressure-sensitive adhesives are well known in the art for bonding to a variety of materials such as glass, metals, painted surfaces, plastics, and the like. Multilayer films, both with and without pressure sensitive adhesive layers, have been described as, for example, films having tear or puncture resistance or mirror-like properties, and tapes. Intermediate layers have been described for use in multi-layered constructions to adhere different polymeric materials that otherwise have insufficient interlayer adhesion. Intermediate layers, or tie layers, generally have an affinity for both of the principal layers. Blends of otherwise incompatible polymers also have been produced using compatibilizers.
Briefly, the present invention provides a composite pressure-sensitive adhesive (PSA) comprising from about 95 to about 5 parts by weight of an acrylic pressure-sensitive adhesive; from about 5 to about 95 parts by weight of an at least partially soluble (in a solvent) polymer selected from the group consisting of a butadiene-containing polymer, an isoprene-containing polymer, a saturated olefin-containing polymer, and a styrene-containing polymer; and a compatibilizer present in the composite pressure-sensitive adhesive in an amount greater than 0 to about 10 parts by weight of the composite pressure-sensitive adhesive, the compatibilizer having a structure selected from the group consisting of (1) an acrylic adhesive-compatible segment and a polymer-compatible (i.e., compatible with the polymer of the composite PSA) segment wherein at least a portion of the compatibilizer is present substantially throughout either the acrylic adhesive, the polymer, or both, and (2) an acrylic adhesive-reactive segment and a polymer-compatible segment wherein at least a portion of the compatibilizer is present substantially throughout the polymer.
In this description, xe2x80x9ccompatiblexe2x80x9d means that materials form thermally stable non-equilibrium morphologies during processing that do not significantly coalesce into separate phases or increase in domain size upon aging at temperatures at or above the glass transition temperatures (Tg) or melting transition temperatures (Tm) of the materials.
A xe2x80x9ccompatible mixturexe2x80x9d refers to a material capable of forming a dispersion in a continuous matrix of a second material, or capable of forming a co-continuous polymer dispersion of both materials.
xe2x80x9cCompatibilizerxe2x80x9d means a material comprising less than about 10 weight percent of at least one phase of a system having two or more phases, that improves the interfacial adhesion between two otherwise immiscible material phases. The compatibilizer is present throughout at least one phase, it is preferentially present at an interface between at least two of the phases, and it increases the compatibility of at least two of the phases in the system. If the weight ratio of the compatibilizer in the system is too high relative to the other phases, a portion of it may separately form a distinct phase.
xe2x80x9cMisciblexe2x80x9d as used for a polymer blend, means any blend having a free energy of mixing less than zero, and xe2x80x9cimmisciblexe2x80x9d as used for a polymer blend, means any blend having a free energy greater than zero. A miscible polymer is capable of forming a blend with a second material, which blend appears to be a single phase with no apparent phase separation, and such capability may depend on the temperature of the blend.
xe2x80x9cReactivexe2x80x9d means that components are capable of forming a chemical bond, which may be covalent or ionic.
xe2x80x9cCopolymerxe2x80x9d means a block, graft or random copolymer.
xe2x80x9cCrosslinkxe2x80x9d means an element, group, or compound that attaches two chains of polymer molecules, primarily through chemical bonding.
xe2x80x9cContinuousxe2x80x9d means an uninterrupted phase of a component; xe2x80x9cdiscontinuousxe2x80x9d means a discrete phase dispersed within a continuous phase; and xe2x80x9cco-continuousxe2x80x9d means a multiphase morphology of a dispersion or blend of two or more components, wherein each component in the blend is essentially continuous in nature, and the pattern(s) of one or more phases may be irregular or complex.
The present invention provides improved adhesive properties including 180xc2x0 peel adhesion, cohesive strength, shear strength, and a non-equilibrium morphology that is more thermally stable than similar compositions without compatibilizer. The present invention also provides improved interlayer adhesion in multilayer embodiments of the invention. The present invention further provides improved layer stability when multilayer embodiments are aged at elevated temperatures.